My son lives in a State where you are not allowed to use a rifle during deer. One of his options is shooting shotgun slugs. He owns an old Model 1100 20ga, Skeet. He recently ordered a rifled choke tube and attempted to replace the tube that was in the gun. The new rifled choke will not fit. It is actually slightly larger in diameter then the barrel opening. I asked if he may have received a 12ga choke by accident and he stated that the choke tube states that is a 20ga? Can anyone provide an explanation why this choke tube will not fit? I have not seen the barrel or the tube.